Pump redundancy for optical amplifiers

Abstract

Currently laser diode pump redundancy for an optical fiber amplifier is obtained by selectively connecting one of two diode pumps to an optical amplifier via an optical switch. When the diode laser pump which is connected to the amplifier becomes defective, the optical switch is activated, either remotely or automatically, and the good laser diode is substituted for the defective laser diode pump. In another arrangement, two laser diodes are coupled to an optical fiber amplifier via a polarization-dependent optical coupler. In each instance, a second laser diode is required to provide pump redundancy for an optical fiber amplifier. In this invention, at least, two laser diodes are coupled via a 3 dB optical coupler to supply pump power to each of the two optical fiber amplifiers simultaneously. If one of the laser diode pumps fails, the other laser diode pump provides pump power to each of the optical fiber amplifiers. Thus, with the addition of a 3 dB coupler, pump redundancy for a pair of optical fiber amplifiers is obtained with only two laser diode pumps instead of the normally required four laser diode pumps. In practice, only one of the two pumps can be active, and the other turned on only when the first pump fails. In another embodiment, the two laser diode pumps can be active at all times where each laser diode pump is operated at either full or less than full power. In the arrangement where the laser diode pumps are operated simultaneously at less than full power, when a pump failure occurs the power output of the good laser diode pump can be increased to compensate for the loss of power from the defective pump.

We claim: 
     
       1. Optical fiber amplifiers having pump redundancy comprising a first doped optical fiber, an input port adapted to couple optical signals to said first doped optical fiber,   an output port coupled to receive the signal amplified by said first doped optical fiber,   a first directional coupler adapted to couple pump power to said first doped optical fiber,   a second doped optical fiber,   an input port adapted to couple optical signals to said second doped optical fiber,   an output port coupled to receive the signal amplified by said second doped optical fiber,   a second directional coupler adapted to couple pump power to said second doped optical fiber,   a laser diode pump source, and   coupler means interposed between said laser diode pump source and said first and second directional couplers to couple pump power from said laser diode pump source to said first and second doped optical fibers simultaneously.   
     
     
       2. The structure of claim 1 wherein said first and second optical fibers are doped with erbium.   
     
     
       3. The structure of claim 1 wherein said coupler means comprises a directional coupler.   
     
     
       4. The structure of claim 3 wherein said directional coupler is a 3 dB coupler.   
     
     
       5. The structure of claim 1 wherein said laser diode pump source comprises a first laser diode and a second laser diode.   
     
     
       6. The structure of claim 5 wherein said first and second laser diodes are coupled to operate sequentially.   
     
     
       7. The structure of claim 5 wherein said first and second laser diodes are coupled to operate simultaneously at reduced power until one of the laser diodes experiences a failure whereupon the other laser diode is operated at increased power.